Multi‐fluid code simulations including anomalous non‐diffusive transport of plasma and impurities in the tokamak SOL

Abstract

AbstractFast intermittent transport has been observed in the scrape‐off layer (SOL) of major tokamaks including Alcator C‐Mod, DIII‐D, and NSTX. This kind of transport is not diffusive but rather convective. It strongly increases plasma flux to the chamber walls and enhances the recycling of neutral particles in the main chamber. We discuss the anomalous cross‐field convection (ACFC) model for impurity and main plasma ions and its relation to intermittent transport events, i.e. plasma density blobs and holes in the SOL. Along with plasma diffusivity coefficients, our transport model introduces time‐independent anomalous convective velocities across the confining magnetic field. In the discharge modeling, diffusivity coefficients and ACFC velocity profiles are adjusted to match a set of representative experimental data. We use this model in the edge plasma physics code UEDGE to simulate the multi‐fluid two‐dimensional transport for these three tokamaks. We present simulation results suggesting the dominance of anomalous convection in the far SOL transport. These results are consistent with the hypothesis that the chamber wall is an important source of impurities and that different impurity charge states have different magnitude and sign of their anomalous radial convective velocities. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)